This guy needs some help... seen on the way to work today.

O- is the universal donor for blood and organs which means that someone with O- can give blood and organs to people of blood types O, A, B, and AB, including all plus/minus variations. O+ are not universal donors despite being type O, because they can't donate to the O- type. However, the downside is that O- cannot receive blood or organs from any other blood type.

Likewise that means that if you have a blood type like AB+, which is the universal receiver for blood and organs, is that your body can pretty much take blood and organs from anyone. There are other factors they look at when determining compatibility, but being AB+ means the pool of potential donors is much larger.

And since it's extremely unlikely a random living person will give you an important organ like a liver lobe, lung or kidney, your only hope is that someone who is O-, and an organ donor, will die with a healthy version of the organ you need. To top it off, the organ needs to be relatively close by(they don't keep long), and there may be(read: will be) people ahead of you waiting on the same organ.

Given the chart you linked, in the US the potential pool of donors breaks down like this:

O- : 7% of the population(can receive from O- only)

O+ : 44.4%(can receive from O-, O+)

B- : 45.9%(can receive from O-, O+, B-)

B+ : 54.4%(can receive from O-, O+, B-, B+)

A- : 50.7%(can receive from O-, O+, A-)

A+ : 86.4% (can receive from O-, O+, A-, A+)

AB- : 96.6% (can receive from O-, O+, A-, A+, B-, B+)

AB+ : 100% (can receive from all blood types)

So O- folks start out with the smallest pool of potential donors, and then you have to pile on all of the other requirements for a donation. There are many conditions that require a donation quickly(within weeks), and the right donor might come by every few months.

As you can see from the above, pretty much everyone but O- can draw organs from half the population or more. O- is closer to 1/15th of the population.